ZMF Atrium - new open-back co-flagship

[Monsterzero]

I have an OTL on my desk that probably weighs 25lbs and looks like it came straight out of Hellraiser.

photos or it didn't happen

 

[L0rdGwyn]

photos or it didn't happen

Same old spinosaurus! I figure people are tired of my amplifier pics lol I am out so here's the last one I took. Gotta be careful when I move it, dropping on my foot would be very bad.

 

[jinxy245]

I figure people are tired of my amplifier pics

Never.

 

[sp33ls]

While I say that I'm not tempted to go beyond my BH C2A, @L0rdGwyn consistently entices myself into going deeper down the DIY OTL rabbit hole lol.

Which build forum/threads would you recommend -- DIYA & Audiokarma? I know there's a lot of different designs out there to explore. I'd like to check out some which are predominant in 2nd order, low 3rd order, and next to no high order distortion. Negative phase 2nd I think is usually my preference.

 

[Guinibee]

They convinced me to buy the BHC+SB and I will build it while burn-in the Atriums. Even being my first time soldiering, I will not think anymore, I will learn at the same time and I just will do it well. Also, I wanted to learn to weld since long time

Oh nice I see you have a BF2 and Jot 2 as well! We're basically in the same boat!

 

[Monsterzero]

Same old spinosaurus! I figure people are tired of my amplifier pics lol I am out so here's the last one I took. Gotta be careful when I move it, dropping on my foot would be very bad.

Well, this thread will most likely be seeing a lot of this amp too, so theres that....

The Glacier, which replaces my Glenn OTL. This amp stages like crazy, coupled with the Atrium I will never have to drink ayahuasca again

 

[Pharmaboy]

I will never have to drink ayahuasca again

I had to google this.

What a wild reference to make in an Atrium post!

 

[Monsterzero]

I had to google this.

What a wild reference to make in an Atrium post!

Alas, I never did make it down to the Amazon in my younger days, and I do believe the ship has already sailed, but you need to come up this summer and hear this amp with the Atrium.

It's already the best I've ever heard the VO sound. I'm suspecting the Atrium will be no different

 

[L0rdGwyn]

While I say that I'm not tempted to go beyond my BH C2A, @L0rdGwyn consistently entices myself into going deeper down the DIY OTL rabbit hole lol.

Which build forum/threads would you recommend -- DIYA & Audiokarma? I know there's a lot of different designs out there to explore. I'd like to check out some which are predominant in 2nd order, low 3rd order, and next to no high order distortion. Negative phase 2nd I think is usually my preference.

The C2A is a great amp! I owned one at one point. diyAudio is definitely the #1 place for DIY tube knowledge on the web. I can't necessarily recommend a specific build or thread, I'm sure there are some great ones out there, I just don't know of them! But generally I think the good old fashioned cathode follower output sounds great, making the BHC a good starting framework. The same general circuit is in the BHC, DarkVoice, La Figaro 339, Elise, Euforia and others, just with different twists.

I think if you wanted to upgrade from the C2A, the way to go would be to build something that has higher transconductance / lower output impedance in the cathode follower output stage. The easiest way to do that is to use a pair of 6AS7G / 6080 (as has been done many times) and parallel the sections of the tube, which doubles the transconductance and halves the output impedance. The challenge with that is handling the doubled current in the power supply (i.e. heat management). Could also pursue other tubes that have a higher transconductance. I think active loading in both the input and output stages makes a big difference. Heat management becomes a challenge again in the output stage if active loading given the high bias current of the 6AS7G. Another option would be to use a choke there instead. Lots of different approaches, I'm sure a quick search on diyAudio would give you a ton of hits. Happy to answer questions if you find something you like.

(Side note: I have maybe...eight? of those THF-51S SITs, actually had a design all planned out for them! Basically went tube gain stage > JFET buffer > choke loaded common drain THF-51S output. Think it was a pretty good idea, have the schematics somewhere on my computer, but I keep getting distracted by tube projects).

Well, this thread will most likely be seeing a lot of this amp too, so theres that....

The Glacier, which replaces my Glenn OTL. This amp stages like crazy, coupled with the Atrium I will never have to drink ayahuasca again

Huh, looks familiar. Awful decorating in that house.

 

[erics75]

Is the BHC w/speedball really that good? I know how to solder and I bet I could build it, I just really don't have much time these days . I was wondering about Feliks Echo MK2 or Woo Audio WA6 (both around $1000). It's a bit higher than I would like, especially if I'm only getting minor differences than a $300 range Valhalla 2 or Xduoo TA-26. If I went that high I'd probably try to sell my Lyr 3 since it would be a bit redundant. I figure I can get around $400 for the Lyr and if I add another $600 I could maybe reach for the Echo or WA6, but I want to know those are significant upgrades, otherwise it wouldn't be worth it. My wife already hates I spent as much as I did to get the Atrium lol.

Sorry been a crazy day at work. Yeah the BHC is insanely good. It was my first real foray into true tube amps, and I've never looked back. You could try putting a Wanted ad in the classifieds for one, you never know.

 

[Pharmaboy]

Alas, I never did make it down to the Amazon in my younger days

Neither did I. But I found other ways to sample psychedelics.

Probably one of the reasons I'm now using an involuntary-donor brain...

 

[L0rdGwyn]

Neither did I. But I found other ways to sample psychedelics.

Probably one of the reasons I'm now using an involuntary-donor brain...

I hope your donor wasn't named Abby Normal.

 

[rustydabear]

But you didn't see the cons in small print: "Prepare to empty

The C2A is a great amp! I owned one at one point. diyAudio is definitely the #1 place for DIY tube knowledge on the web. I can't necessarily recommend a specific build or thread, I'm sure there are some great ones out there, I just don't know of them! But generally I think the good old fashioned cathode follower output sounds great, making the BHC a good starting framework. The same general circuit is in the BHC, DarkVoice, La Figaro 339, Elise, Euforia and others, just with different twists.

I think if you wanted to upgrade from the C2A, the way to go would be to build something that has higher transconductance / lower output impedance in the cathode follower output stage. The easiest way to do that is to use a pair of 6AS7G / 6080 (as has been done many times) and parallel the sections of the tube, which doubles the transconductance and halves the output impedance. The challenge with that is handling the doubled current in the power supply (i.e. heat management). Could also pursue other tubes that have a higher transconductance. I think active loading in both the input and output stages makes a big difference. Heat management becomes a challenge again in the output stage if active loading given the high bias current of the 6AS7G. Another option would be to use a choke there instead. Lots of different approaches, I'm sure a quick search on diyAudio would give you a ton of hits. Happy to answer questions if you find something you like.

(Side note: I have maybe...eight? of those THF-51S SITs, actually had a design all planned out for them! Basically went tube gain stage > JFET buffer > choke loaded common drain THF-51S output. Think it was a pretty good idea, have the schematics somewhere on my computer, but I keep getting distracted by tube projects).



Huh, looks familiar. Awful decorating in that house.

Question for you all with tube amp knowledge and how the pair with ZMF:
I just purchased my first tube amp- got a lightly used dark voice with updated tubes:
Natural sound CV 181 T
Flying C CH13C

Enjoying the sound.
My Atrium and Verite closed both sound great on it.
1. Would I get a huge improvement from a Bottlehead with speedball?
2. what is better about the crackatoa?
3. The mainline looks really interesting as I would like balanced also if possible.
Is the mainline much more difficult to build?
Is it worth the price?

Thanks for your input..

 

[L0rdGwyn]

Question for you all with tube amp knowledge and how the pair with ZMF:
I just purchased my first tube amp- got a lightly used dark voice with updated tubes:
Natural sound CV 181 T
Flying C CH13C

Enjoying the sound.
My Atrium and Verite closed both sound great on it.
1. Would I get a huge improvement from a Bottlehead with speedball?
2. what is better about the crackatoa?
3. The mainline looks really interesting as I would like balanced also if possible.
Is the mainline much more difficult to build?
Is it worth the price?

Thanks for your input..

Hello! I think you would get an improvement going from the DarkVoice to the BHC+SB. The BHC+SB uses something called constant current source loading of both the 12AU7 input and the 6080 output, which translates to a higher degree of clarity, soundstage, detail retrieval with lower distortion. The DarkVoice uses more standard resistor loading and is more similar to the stock BHC without SB (although not exactly the same).

The Crackatwoa is a BHC+SB but includes a shunt regulated tube power supply. A shunt regulator will reduce power supply noise, hum, and overall will give the amplifier a "blacker background". It also includes additional inputs and dedicated space for large film output capacitors if the builder wants to add them at some point.

The Mainline by comparison is not an OTL, it is a transformer coupled amplifier using an output topology called parafeed. I won't bore with the technical details, but basically the output from the tube goes through a capacitor, then to the output transformer while also being constant current source loaded, similar to the SB addition to the BHC. This type of design will get you a more "clean" and "transparent" sound relative to an OTL like the BHC+SB. It is also a "spud" amplifier, meaning there is only one tube in the signal path, a single tube gain stage. On top of that, it also has a shunt regulated power supply, similar to the Crackatwoa. I have not heard the Mainline myself actually, but I have designed and built similar parafeed amplifiers, the sound of this topology is very good. The Mainline is more complex to build, but I think if you are careful and up to the challenge, you can do it no problem. As I've said, Bottlehead has very good directions, but the Mainline will require more soldering and overall will take longer to build than the BHC+SB. The skills required, however, are the same.

The major advantage of the Mainline, or any other transformer coupled amplifier, is the transformer can match the output impedance of the tube stage to various headphone impedances, allowing the use low impedance / current demanding headphones, like planar magnetics. As you can see in the photos, it has an impedance switch for both high and low impedance headphones.

One other note - the Mainline does not have balanced inputs, only single-ended inputs. The outputs can be changed from single-ended to balanced. Note however this is not a "balanced amplifier", the balanced output is done via the output transformer, rather than the circuit topology itself being balanced. It is a single-ended amplifier.

If you want something more "clean" and "transparent", headphone pairing flexibility and are up for more soldering, Mainline could be a good choice. If you want a more simple build, a more "euphonic" character, and only plan to use high impedance dynamics, then the BHC+SB is a good option. Could always go with the BHC+SB and then upgrade to the Mainline down the road.

 

[rustydabear]

Hello! I think you would get an improvement going from the DarkVoice to the BHC+SB. The BHC+SB uses something called constant current source loading of both the 12AU7 input and the 6080 output, which translates to a higher degree of clarity, soundstage, detail retrieval with lower distortion. The DarkVoice uses more standard resistor loading and is more similar to the stock BHC without SB (although not exactly the same).

The Crackatwoa is a BHC+SB but includes a shunt regulated tube power supply. A shunt regulator will reduce power supply noise, hum, and overall will give the amplifier a "blacker background". It also includes additional inputs and dedicated space for large film output capacitors if the builder wants to add them at some point.

The Mainline by comparison is not an OTL, it is a transformer coupled amplifier using an output topology called parafeed. I won't bore with the technical details, but basically the output from the tube goes through a capacitor, then to the output transformer while also being constant current source loaded, similar to the SB addition to the BHC. This type of design will get you a more "clean" and "transparent" sound relative to an OTL like the BHC+SB. It is also a "spud" amplifier, meaning there is only one tube in the signal path, a single tube gain stage. On top of that, it also has a shunt regulated power supply, similar to the Crackatwoa. I have not heard the Mainline myself actually, but I have designed and built similar parafeed amplifiers, the sound of this topology is very good. The Mainline is more complex to build, but I think if you are careful and up to the challenge, you can do it no problem. As I've said, Bottlehead has very good directions, but the Mainline will require more soldering and overall will take longer to build than the BHC+SB. The skills required, however, are the same.

The major advantage of the Mainline, or any other transformer coupled amplifier, is the transformer can match the output impedance of the tube stage to various headphone impedances, allowing the use low impedance / current demanding headphones, like planar magnetics. As you can see in the photos, it has an impedance switch for both high and low impedance headphones.

One other note - the Mainline does not have balanced inputs, only single-ended inputs. The outputs can be changed from single-ended to balanced. Note however this is not a "balanced amplifier", the balanced output is done via the output transformer, rather than the circuit topology itself being balanced. It is a single-ended amplifier.

If you want something more "clean" and "transparent", headphone pairing flexibility and are up for more soldering, Mainline could be a good choice. If you want a more simple build, a more "euphonic" character, and only plan to use high impedance dynamics, then the BHC+SB is a good option. Could always go with the BHC+SB and then upgrade to the Mainline down the road.

Wow- thank you for such a comprehensive answer to my questions. I appreciate you taking the time. Going to read this through a couple of times and I am sure I will have another question for you. Thanks for helping to clear the fog a little.